Compared to when they used the sham filter, the seniors’ average exposure to PM2.5 indoors was 31 percent lower with the low-efficiency filter and 53 percent lower with the HEPA filter.

And with use of the air filters, blood pressure levels in people with hypertension improved by an amount similar to what might be achieved with lifestyle changes like increased exercise or reduced salt consumption, said lead study author Masako Morishita of Michigan State University in East Lansing.

“A simple intervention using inexpensive indoor air filtration units can help to lower both PM2.5 exposures and blood pressure levels,” Morishita said by email. “Since hypertension is the leading risk factor for death worldwide, we believe much larger trials are warranted to test whether air filtration units can play an important role in helping to prevent cardiovascular diseases worldwide.”

The World Health Organisation attributes four million deaths a year to fine particulate matter exposure. Its guidelines recommend against average exposure above 10 micrograms per cubic meter of air (ug/m3), the authors note. In this study, the average exposure was 15.5 ug/m3 without air filtration, 10.9 ug/m3 with low-efficiency filtration, and 7.4 ug/m3 with HEPA filters.